Why do electric motors need comprehensive protection devices, and what are their typical components? During actual operation, electric motors often burn out or switches fail due to overload and other conditions. Therefore, to effectively prevent these problems, protective devices must be installed. Common protective devices include fuses and thermal relays. Fuses are mainly used for short-circuit protection and can reliably protect against prolonged overloads and phase loss; while thermal relays are often infrequent due to frequent changes in environment and equipment, untimely settings, lack of calibration, and inaccurate operating values. Therefore, to ensure the safe operation of electric motors, a comprehensive electric motor protection device is necessary.
A comprehensive motor protection device generally consists of the following parts:
1. Filtering circuit. The task of this circuit is to detect the changes in current and voltage generated when the motor experiences overcurrent, phase loss, or short circuit using sensing elements.
2. Adjustment circuit. Used to change the operating parameters of the protection device, and set according to different loads.
3. Start-up circuit. After identifying and comparing incoming current or voltage signals, it determines whether there is an output.
4. Identification circuit. This typically uses transistor switching circuits, silicon controlled rectifier (SCR) switching circuits, etc.
